1. Field of the Invention
This invention relates to an uninterruptible power supply device for supplying backup power to electronic equipment such as a computer in case of interruption of power supply from a power source, and more particularly, to an interruptible power supply device which is configured to save electric power.
2. Description of the Related Art
If electronic equipment using commercial power (alternating-current power) as a power source, such as personal computers or servers, undergoes a momentary interruption or outage of power supply during operation thereof, various inconveniences can be caused such as the occurrence of error in the processing operation itself or the loss of valuable processing data. Accordingly, various attempts have been made to eliminate such inconveniences, as disclosed in Unexamined Japanese Patent Publications Nos. 2002-27683 and 2002-258993 in which a power supply system for this kind of electronic equipment is provided with an uninterruptible power supply device including a rechargeable battery, and in case of outage of commercial power supply (external power source), backup power is supplied from the rechargeable battery to the electronic equipment to ensure continued processing operation of the equipment and to protect processing data.
Such an uninterruptible power supply device is generally configured such that the rechargeable battery is charged by electric power from commercial power supply, and in case of power outage, the rechargeable battery supplies (discharges) the power stored therein to the electronic equipment to thereby provide backup power necessary for the operation of the electronic equipment. Also, in order to prevent wasteful consumption of the power stored in the rechargeable battery, the uninterruptible power supply device is often configured so as to stop its operation after supplying power to the electronic equipment for a period of time necessary for the equipment to complete a predetermined process such as saving of data, for example.
In the case where the operation of the uninterruptible power supply device is stopped after a lapse of the backup period as mentioned above, the rechargeable battery status monitoring function performed by the uninterruptible power supply device also stops, with the result that the charge state of the rechargeable battery cannot be monitored thereafter. As an alternative measure, information about the status (battery voltage, remaining capacity, etc.) of the rechargeable battery, for example, may be saved in a nonvolatile memory such as EEPROM or flash memory when the operation of the uninterruptible power supply device is stopped. Writing data in this type of nonvolatile memory, however, requires substantial time. Moreover, if the uninterruptible power supply device is not restarted for a long time (e.g., several months or more), there arises a marked discrepancy between the battery status stored in the nonvolatile memory and the actual status of the rechargeable battery due to self-discharge thereof.